It is well known that rubbers are permeable to gases. As such the use of rubber in articles of manufacture such as hoses, tires and airsprings has presented a problem of gas retenion over the years. One approach to achieving enhanced air retention in a rubber article, such as a tire, has been to line the interior of the tire with an innerliner such as bromobutyl rubber.
In an effort to achieve a reduction in the total tire weight it has been proposed to eliminate the innerliner compound. The primary purpose of this innerliner component is to maintain tire air pressure and the innerliner compounds have been formulated with the intention of low air permeability in mind. However, there are problems associated with the manufacture of tires using a bromobutyl rubber innerliner; one of which is the high cost of the bromobutyl rubber. Other problems include air trapped between plies, adhesion to the stock contained in the tire and the adhesion of the bromobutyl innerliner to the curing bladder during the vulcanization process. In an effort to eliminate the use of these innerliners, a process has been proposed to reduce the air permeability of the carcass compound. A portion of the instant invention is directed to a process for directly modifying the surface of a rubber compound so as to enhance its ability to prevent the transmission of gaseous materials therethrough. A direct rubber surface modification technique would be valuable since the bulk physical properties of the rubber compound would remain unaffected and such an application could be readily incorporated into tire manufacturing either to a green calendared compound, to the green tire or to the cured tire.
In an effort to enhance the antipermeability of rubber compounds, the inventors herein have investigated numerous techniques and procedures which would afford an air impermeable barrier and allow for the reduction in total tire weight.
U.S. Pat. No. 3,632,400 describes a process for coating a surface of a rubber article comprising the in situ formed polymerization product of a compound such as 1,1-dihydroheptafluorobutyl acrylate which is bonded to the rubber surface through use of an electron beam having an average potential of about 100,000 volts. Through this radiation grafting of fluorine containing acrylates the patent discloses that the elastomer has improved solvent resistance, abrasion resistance, low coefficient of friction, is oxidatively stable and is thermally stable.
U.S. Pat. No. 3,793,298 is concerned with a method for halogenizing surfaces of synthetic and/or natural rubber materials. Specifically the '298 patent is concerned with a method for halogenating surfaces of a rubber with a halogen donor to make such surfaces better glueable to rubber or their materials. The process disclosed therein comprises contacting the rubber with an acidified solution of a N-halogen sulfonamide in an organic solvent in which said sulfonamide is soluble and which is substantially inert to the action of the halogen. After application of the solution to the rubber substrate the solvent is evaporated and the surface is thus halogenated so as to enhance the adhesion between the rubber and other materials.
Canadian Pat. No. 931,907 is concerned with the treatment of polychloroprene rubber with radiation having a wavelength between 2,000 and 3,500 Angstroms. The resulting articles have extremely low coefficients of friction, but retain their normal flexibility and hardness properties. This Canadian patent further teaches that including small amounts of surfactant in the compounding of the rubber produces a still lower coefficient of friction after radiation. In addition, this Canadian patent teaches that instead of compounding the surfactant into the elastomer, the surfactant may be coated on the formed article prior to irradiation. The materials coated on the rubber such as perfluoroalkyl sulfonate surfactants have been found to be useful.
Chemical Abstracts 90: 7327d discloses that in contrast to thermal chlorination, fluorination, or sulfochlorination at 80.degree. C. the radiation initiated reactions of nitrile rubber, butadiene rubber, neoprene rubber and EPDM with chlorine and fluorine give elastic surfaces. These reactions are gas diffusion rate-controlled and occur only on the surface of the rubbers. This article is primarily concerned with the surface treatment of rubbers through the use of gaseous molecular halogens.
Chemical Abstracts, 81: 64889b discusses the chlorination of butyl rubber by gaseous chlorine in the presence of dibenzoylperoxide and ultraviolet radiation. This process introduces .dbd.CHCl and --CH.sub.2 Cl groups into the rubber molecule.
U.S. Pat. No. 3,968,316 discloses a process for the surface treatment of a rubber or synthetic resin containing ethylenic unsaturation by contacting the rubber or resin with an alkyl hypohalite and a compound containing an active halogen and a functional group thereby improving or providing the rubber or resin with improved properties such as adhesion, printability, dyeability, flame retardation, antistatic properties, ion-exchangeability and antipermeability.
U.S. Pat. No. 3,940,548 is concerned with the process for treating the surfaces of shaped articles of rubber which comprises contacting the surfaces of the shaped rubber articles containing carbon to carbon unsaturated double bonds with an alkyl hypohalite. The alkyl hypohalites used for the surface treatment include the tertiary alkyl hypohalites such as tertiary butyl hypohalite, tertiary amyl hypohalite and the like. The process disclosed in the '548 patent requires the immersion of the rubber article in a solution of the tertiary hypohalite after which the sheets are washed and then dried.
The prior art does not suggest or disclose the instant invention which provides a simple process for enhancing numerous physical properties of a rubber through the treatment with an alkyl halide and the subsequent irradiation with ultraviolet-visible light.